The Introduced Free-ranging Rhesus and Patas Monkey Populations of Southwestern Puerto Rico

Abstract

Rhesus (Macaca mulatta) and patas (Erythrocebus patas) monkeys escaped to the mainland of southwestern Puerto Rico (SWPR) from research colonies on small offshore islands during the 1960s and through 1982. A three year study (1990-1993) combined radio-telemetry with visual observations to collect information on population sizes, the composition of social groups, their daily movements, and their home ranges. Two populations of rhesus monkeys were identified in SWPR: one within the study area in Sierra Bermeja and a second population located 10 km north of the study area. The size of the Sierra Bermeja rhesus population was derived from escapees from research colonies and at the time of the study was 65-85 individuals. Within their home range area (3.7km2) the density of this population was »18.9 individuals/km2. A second rhesus population was found in a mountainous region 10 km north of the study area. This population consisted of one (or two) heterosexual groups with a total of 40-45 individuals. Although a primary characteristic of this species in India is its ability to live as a commensal with humans, the rhesus monkey populations of SWPR are extremely shy and elusive, they avoid contact with humans. The patas monkey population consisted of »120 individuals in four heterosexual groups and several all-male bands. There was no evidence of patas monkeys outside the study area. Within their home ranges (26.8 km2) the population density was 4.47 individuals/km2). Patas monkeys have not previously been considered a territorial species, their behavior in SWPR suggested territoriality. In contrast to studies in Africa, where the amount of home range overlap between patas monkey groups is high, in SWPR the amount of range overlap between groups is small and each group uses areas with clearly defined boundaries.